Glutathione-related antioxidant defenses in human atherosclerotic plaques

Potent induction of cellular antioxidants and phase 2 enzymes by resveratrol in cardiomyocytes: protection against oxidative and electrophilic injury

Resveratrol is known to be protective against oxidative cardiovascular disorders. However, the underlying mechanisms remain unclear. This study was undertaken to determine if resveratrol could increase endogenous antioxidants and phase 2 enzymes in cardiomyocytes, and if such increased cellular defenses could provide protection against oxidative and electrophilic cell injury. Incubation of cardiac H9C2 cells with low micromolar resveratrol resulted in a significant induction of a scope of cellular antioxidants and phase 2 enzymes in a concentration- and/or time-dependent fashion. To investigate the protective effects of the resveratrol-induced cellular defenses on oxidative and electrophilic cell injury, H9C2 cells were first incubated with resveratrol, and then exposed to xanthine oxidase (XO)/xanthine, 4-hydroxy-2-nonenal or doxorubicin. We observed that resveratrol pretreatment afforded a marked protection against the above agent-mediated cytotoxicity in H9C2 cells. Moreover, the resveratrol pretreatment led to a great reduction in XO/xanthine-induced intracellular accumulation of ROS. Taken together, this study demonstrates that resveratrol induces antioxidants and phase 2 enzymes in cardiomyocytes, which is accompanied by increased resistance to oxidative and electrophilic cell injury.

Vitamins in human arteriosclerosis with emphasis on vitamin C and vitamin E

INTRODUCTION

This review focuses on the process of arteriosclerosis arising from oxidative stress on lipoproteins and the general failure of randomized human trials using vitamins to retard this process.

REVIEW

As well as clinical trials, the paper reviews the mechanisms by which a variety of oxidants act. Antioxidants are discussed, emphasizing interactions of vitamins C and E with transition metals that can lead to prooxidation. There is a focus on interactions between supplemental or co-antioxidants that counterbalance prooxidant effects of one another.

CONCLUSIONS

It is concluded that normal cellular supplementation mechanisms are poorly accessible in the arteriosclerotic plaque leading to a prooxidant environment in which the haphazard introduction of vitamins could potentially be hazardous. Continued investigations into basic and clinical redox interactions of the kind discussed in this review using new measuring techniques may lead to approaches whereby antioxidants can be introduced into tissue in controlled ways for reducing arteriosclerosis.

Activity of antioxidant enzymes in children from families at high risk of premature coronary heart disease

A positive family history of coronary heart disease (CHD) is one of the most predictive risk factors of CHD. Many children with increased risk of CHD because of their positive family history of CHD do not present other risk factors, such as altered serum lipid profile. Oxidative stress plays an important part in the pathogenesis of atherosclerosis. Serum antioxidants and intracellular enzymatic antioxidants composed mainly of glutathione peroxidase (GSH-Px), catalase (CAT), superoxide dismutase (SOD) and glutathione reductase counterbalance oxidative stress. Diminished activity of this system may lead to accelerated progression of atherosclerosis. The aim of this study was to assess the activity of CAT, GSH-Px, SOD and glutathione reductase in children with a family history of premature CHD who did not present any other major risk factors of CHD (diabetes, obesity, dyslipidaemia or hypertension). Twenty-two healthy children from high-risk families, selected according to the National Cholesterol Education Program definition, were enrolled in the study. The control group comprised 18 children without a family history of CHD. All the children were healthy and had been screened for hyperlipidaemia, diabetes, hypertension and obesity prior to the study. The erythrocyte activity of CAT, GSH-Px, SOD and glutathione reductase was assessed. Children at high risk of CHD had a statistically significant lower level of GSH-Px and CAT activity than the children in the control group. There were no statistically significant differences in the activity of SOD and glutathione reductase.

Glutathione peroxidase 1 activity and cardiovascular events in patients with coronary artery disease

BACKGROUND

Cellular antioxidant enzymes such as glutathione peroxidase 1 and superoxide dismutase have a central role in the control of reactive oxygen species. In vitro data and studies in animal models suggest that these enzymes may protect against atherosclerosis, but little is known about their relevance to human disease.

METHODS

We conducted a prospective study among 636 patients with suspected coronary artery disease, with a median follow-up period of 4.7 years (maximum, 5.4) to assess the risk of cardiovascular events associated with base-line erythrocyte glutathione peroxidase 1 and superoxide dismutase activity.

RESULTS

Glutathione peroxidase 1 activity was among the strongest univariate predictors of the risk of cardiovascular events, whereas superoxide dismutase activity had no association with risk. The risk of cardiovascular events was inversely associated with increasing quartiles of glutathione peroxidase 1 activity (P for trend <0.001); patients in the highest quartile of glutathione peroxidase 1 activity had a hazard ratio of 0.29 (95 percent confidence interval, 0.15 to 0.58; P<0.001), as compared with those in the lowest quartile. Glutathione peroxidase 1 activity was affected by sex and smoking status but retained its predictive power in these subgroups. After adjustment for these and other cardiovascular risk factors, the inverse association between glutathione peroxidase 1 activity and cardiovascular events remained nearly unchanged.

CONCLUSIONS

In patients with coronary artery disease, a low level of activity of red-cell glutathione peroxidase 1 is independently associated with an increased risk of cardiovascular events. Glutathione peroxidase 1 activity may have prognostic value in addition to that of traditional risk factors. Furthermore, increasing glutathione peroxidase 1 activity might lower the risk of cardiovascular events.

Lipid peroxidation and vitamin E in human coronary atherosclerotic lesions

BACKGROUND

We aimed to assess the oxidant/antioxidant status within the ex vivo human coronary endarterectomy samples.

METHODS

To achieve this, we measured products of lipid oxidation (malondialdehyde, 7-ketocholesterol), lipids (cholesterol, cholesteryl esters) and vitamin E in endarterectomy samples.

RESULTS

Content of malondialdehyde in the plaque ranged from 0.23 to 37.36 microg/g. Unesterified cholesterol content ranged from 0.30 to 1.94 mg/g. It was 9.04+/-4.32% of total cholesterol. Total cholesterol content ranged from 1.73 to 23.69 mg/g. Cholesteryl palmitate content ranged from 0.57 to 19.10 mg/g, which is 11.43-60.86% of the total esters (mean+/-SD 40.27+/-18.42%). Cholesteryl oleate content ranged from 0.24 to 5.76 mg/g, being 9.97-21.81% of total esters (mean+/-SD 14.35+/-4.51%). Cholesteryl linoleate content ranged from 1.05 to 8.21 mg/g, being 17.84-45.15% of total esters (mean+/-SD 30.78+/-11.69%). Cholesteryl arachidonate content ranged from 0.51 to 4.20 mg/g, which is 7.56-22.87% of total esters (mean+/-SD 14.60+/-5.60%). The cholesteryl linoleate/cholesteryl oleate ratio (CL/CO) ranged from 1.01 to 4.33. Content of 7-ketocholesterol in the plaque ranged from 0.0 to 577.5 ng/g of wet weight. The 7-ketocholesterol/total cholesterol ratio was 0.003+/-0.003% (range from 0.0% to 0.008%). The 7-ketocholesterol/unesterified cholesterol ratio was 0.024+/-0.023% (range from 0.0% to 0.066%). The plaque content of vitamin E ranged from 0.0 to 40.9 microg/g of wet weight.

CONCLUSION

The present study, comprising measurements of lipids, products of lipid peroxidation and vitamin E in 12 human coronary endarterectomy samples, lends the evidence for ongoing lipid peroxidation within an atherosclerotic lesion.

Glutathione peroxidase 1 genotype is associated with an increased risk of coronary artery disease

OBJECTIVE

Oxidative stress is implicated in the pathogenesis of many human diseases including atherosclerosis. Human glutathione peroxidase 1 (hgpx1) participates in limiting cellular damage caused by oxidation. A characteristic polyalanine sequence polymorphism in exon 1 of hgpx1 produces three alleles with five, six or seven alanine (ALA) repeats in this sequence. The objective of this study was to determine whether hgpx1 genotype is associated with an altered risk of coronary artery disease (CAD).

METHODS

The frequency of the ALA6 allele was determined in 207 men with angiographic evidence of significant CAD compared to a control group (n = 146), by analysing the lengths of polymerase chain reaction fragments containing the ALA repeat polymorphism. Additional information was collected on severity of CAD, presence or absence of a prior acute myocardial infarction (AMI), smoking status, body mass index (BMI) and other clinical data.

RESULTS

There was a significant association between individuals with at least one ALA6 allele and an increased risk of CAD after adjustment for age, BMI and smoking status (odds ratio, 2.07, 95% confidence interval, 1.08-3.99, P = 0.029). However, there was no association between hgpx1 genotype and a previous history of AMI or hgpx1 genotype and severity of CAD.

CONCLUSION

We conclude that individuals possessing one or two ALA6 alleles appear to be at a modest increased risk of CAD. This observation merits further investigation in other patient populations.

Association between the risk of coronary artery disease in South Asians and a deletion polymorphism in glutathione S-transferase M1

South Asians living in Western societies show a greater risk of coronary artery disease (CAD) than the indigenous Caucasian population, probably related to the change to a Westernised lifestyle and an associated genetic susceptibility. Modulation of DNA damage and mutation caused by polymorphisms in detoxification enzymes, including the glutathione S-transferases (GSTs), is a well-established risk factor for tobacco-related carcinogenesis, and a similar change in cellular damage may be involved in the risk of vascular disease associated with tobacco smoking. In this study we examined whether polymorphisms in GST genes influence the risk of CAD in a case-control group of South Asians, following our recent observation of such an association in Caucasians from the same region of the UK. Blood was obtained from 170 patients of South Asian origin admitted for angiographic investigation of chest pain and from 203 controls. Patients were subdivided into those with and without previous acute myocardial infarction (AMI), and DNA was analysed for deletions in the GSTM1 and GSTT1 genes. An association was found between the prevalence of the GSTM1 null genotype and the risk of developing CAD in this study population. The frequency of the null genotype was 52.7% in healthy controls and 41.2% in patients (odds ratio [OR] 0.63, 95% confidence interval [95% CI] 0.42-0.95, p = 0.029). The effect was similar in subjects with or without a prior history of AMI. The association was also independent of smoking history, with both non-smokers and smokers showing a similar pattern of genotype distribution, the frequency of the null genotype being 51.2% in controls versus 37.0% in patients in 'never' smokers (OR 0.56, 95% CI 0.33-0.94, p = 0.037) and 60.0% in controls versus 46.2% in patients in 'ever' smokers (OR 0.57, 95% CI 0.25-1.28, p = 0.223). The association remained after adjusting for age, sex, body mass index and the presence or absence of stenosis. No significant associations were observed between the GSTT1 genotype and cardiovascular disease (chi(2) test, p > 0.1). The results of this study indicate that the GSTM1 null genotype is protective against both CAD and AMI. However, further study is required in order to elucidate the, as yet unexplained, mechanisms underlying this association.

The elephant in uremia: oxidant stress as a unifying concept of cardiovascular disease in uremia

Cardiovascular disease is the leading cause of mortality in uremic patients. In large cross-sectional studies of dialysis patients, traditional cardiovascular risk factors such as hypertension and hypercholesterolemia have been found to have low predictive power, while markers of inflammation and malnutrition are highly correlated with cardiovascular mortality. However, the pathophysiology of the disease process that links uremia, inflammation, and malnutrition with increased cardiovascular complications is not well understood. We hereby propose the hypothesis that increased oxidative stress and its sequalae is a major contributor to increased atherosclerosis and cardiovascular morbidity and mortality found in uremia. This hypothesis is based on studies that conclusively demonstrate an increased oxidative burden in uremic patients, before and particularly after renal replacement therapies, as evidenced by higher concentrations of multiple biomarkers of oxidative stress. This hypothesis also provides a framework to explain the link that activated phagocytes provide between oxidative stress and inflammation (from infectious and non-infections causes) and the synergistic role that malnutrition (as reflected by low concentrations of albumin and/or antioxidants) contributes to the increased burden of cardiovascular disease in uremia. We further propose that retained uremic solutes such as beta-2 microglobulin, advanced glycosylated end products (AGE), cysteine, and homocysteine, which are substrates for oxidative injury, further contribute to the pro-atherogenic milieu of uremia. Dialytic therapy, which acts to reduce the concentration of oxidized substrates, improves the redox balance. However, processes related to dialytic therapy, such as the prolonged use of catheters for vascular access and the use of bioincompatible dialysis membranes, can contribute to a pro-inflammatory and pro-oxidative state and thus to a pro-atherogenic state. Anti-oxidative therapeutic strategies for patients with uremia are in their very early stages; nonetheless, early studies demonstrate the potential for significant efficacy in reducing cardiovascular complications.

Overexpression of heme oxygenase-1 protects smooth muscle cells against oxidative injury and inhibits cell proliferation

To investigate whether the expression of exogenous heme oxygenase-1 (HO-1) gene within vascular smooth muscle cells (VSMC) could protect the cells from free radical attack and inhibit cell proliferation, we established an in vitro transfection of human HO-1 gene into rat VSMC mediated by a retroviral vector. The results showed that the profound expression of HO-1 protein as well as HO activity was 1.8- and 2.0-fold increased respectively in the transfected cells compared to the non-transfected ones. The treatment of VSMC with different concentrations of H2O2 led to the remarkable cell damage as indicated by survival rate and LDH leakage. However, the resistance of the HO-1 transfected VSMC against H2O2 was significantly raised. This protective effect was dramatically diminished when the transfected VSMC were pretreated with ZnPP-IX, a specific inhibitor of HO, for 24 h. In addition, we found that the growth potential of the transfected cells was significantly inhibited directly by increased activity of HO-1, and this effect might be related to decreased phosphorylation of MAPK. These results suggest that the overexpression of introduced hHO-1 is potentially able to reduce the risk factors of atherosclerosis, partially due to its cellular protection against oxidative injury and to its inhibitory effect on cellular proliferation.

Chemical induction of cellular antioxidants affords marked protection against oxidative injury in vascular smooth muscle cells

Extensive evidence suggests that reactive oxygen species are critically involved in the pathogenesis of cardiovascular diseases, such as atherosclerosis and myocardial ischemia-reperfusion injury. Consistent with this concept, administration of exogenous antioxidants has been shown to be protective against oxidative cardiovascular injury. However, whether induction of endogenous antioxidants by chemical inducers in vasculature also affords protection against oxidative vascular cell injury has not been extensively investigated. In this study, using rat aortic smooth muscle A10 cells as an in vitro system, we have studied the induction of cellular antioxidants by the unique chemoprotector, 3H-1,2-dithiole-3-thione [corrected] (D3T) and the protective effects of the D3T-induced cellular antioxidants against oxidative cell injury. Incubation of A10 cells with micromolar concentrations of D3T for 24 h resulted in a significant induction of a battery of cellular antioxidants in a concentration-dependent manner. These included reduced glutathione (GSH), GSH peroxidase, GSSG reductase, GSH S-transferase, superoxide dismutase, and catalase. To further examine the protective effects of the induced endogenous antioxidants against oxidative cell injury, A10 cells were pretreated with D3T and then exposed to either xanthine oxidase (XO)/xanthine, 4-hydroxynonenal, or cadmium. We observed that D3T pretreatment of A10 cells led to significant protection against the cytotoxicity induced by XO/xanthine, 4-hydroxynonenal or cadmium, as determined by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium reduction assay. Taken together, this study demonstrates for the first time that a number of endogenous antioxidants in vascular smooth muscle cells can be induced by exposure to D3T, and that this chemical induction of cellular antioxidants is accompanied by markedly increased resistance to oxidative vascular cell injury.

Oxidant injury in coronary heart disease (Part-I)

Oxidative stress damages the heart through a series of reactions beginning with lipid peroxidation, the main process behind atherosclerosis. Antioxidant supplementation has some beneficial effects by binding with metal ions or catalysts to prevent oxidative lipid peroxidation and chain production.

17-beta estradiol preserves endothelial cell viability in an in vitro model of homocysteine-induced oxidative stress

High levels of homocysteine (Hcy) accelerate endothelial cell damage by producing hydrogen peroxide (H(2)O(2)). We investigated whether 17-beta estradiol may prevent the accelerated rate of endothelial cell detachment and reduced cell viability in cultured endothelial cells challenged with Hcy. Cultured bovine aortic endothelial cells (BAEC) were incubated for 72-h with either vehicle (alcohol) or different concentrations of 17-beta estradiol (1 nM [1E2] and 10 nM [10E2]) before being challenged with 0.5 mM of Hcy. Cell viability and H(2)O(2) levels were evaluated at 30 min, 1-, 2-, 4-, 8-, and 24-h after adding Hcy. Cell suspensions were frozen in liquid nitrogen and used later for spectrophotometric measurement of intracellular glutathione (GSH) levels. Cell viability 24 h after Hcy administration was significantly lower in vehicle versus 1 nM and 10 nM 17-beta estradiol (44 +/- 5% vs. 70.66 +/- 4%, [p < 0.001] and 79 +/- 5% respectively, [p < 0.001]). H(2)O(2) levels were higher in vehicle (1 +/- 0.05 microM) compared with 1E2 and 10E2 (0.8 +/- 0.1 microM, p = 0.02 and 0.1 +/- 0.05 microM, respectively, p < 0.001), whereas GSH content was increased in 1E1 and 10E2 versus control (27.69 +/- 4.6 nM/10(6) cells and 43.49 +/- 5.5 nM/10(6) cells vs. 13.33 +/- 1.5 nM/10(6) cells, p < 0.001). Bovine aortic endothelial cells treatment with 17-beta estradiol (0, 1, and 10 nM) and 0.1 mmol buthionine sulfoximine, an inhibitor of gamma-glutamylcysteine synthase, abolished the beneficial effects of estradiol alone on cell viability, GSH content, and H2O2 generation. Estradiol prevents Hcy-induced endothelial cell injury by increasing the intracellular content of GSH.

Plasma aminothiol oxidation in chronic hemodialysis patients

BACKGROUND

Plasma aminothiols, including homocysteine, cysteine, and glutathione, function as an important extracellular redox system. We examined the plasma aminothiol concentration and redox status in ten chronic hemodialysis patients compared to ten age-matched healthy subjects.

METHODS

Plasma levels of reduced, free oxidized, and protein-bound homocysteine, cysteine, cysteinylglycine, and glutathione were determined using high-pressure liquid chromatography (HPLC).

RESULTS

Total plasma homocysteine, cysteine, and cysteinylglycine levels were significantly elevated in hemodialysis patients before dialysis compared to healthy subjects. Total plasma concentration of cysteine and homocysteine significantly decreased after hemodialysis. The ratio of free oxidized to free reduced homocysteine, cysteine, cysteinylglycine, and glutathione were each significantly elevated before dialysis compared to healthy subjects, and decreased significantly by the end of dialysis. The free oxidized to reduced ratio of cysteine and homocysteine were also significantly correlated with total plasma concentrations.

CONCLUSIONS

Plasma aminothiols are excessively oxidized in uremia, while the hemodialysis procedure is restorative of redox status. Oxidized aminothiols are candidate uremic toxins.

Predicting plaque rupture: enhancing diagnosis and clinical decision-making in coronary artery disease

Atherosclerosis is the process underlying coronary artery disease, myocardial infarction and cerebrovascular disease and is a leading cause of morbidity and mortality in industrialized countries. The atherosclerotic plaque is often indolent and progressive and may destabilize without warning. Components of the atherosclerotic plaque, including structural, cellular and molecular characteristics, determine its vulnerability to rupture. The imaging techniques currently available utilize invasive and non-invasive methods to characterize coronary artery stenoses. Detection, however, usually occurs late in the course of disease after symptoms have presented. Much effort has recently been directed at early detection and in defining markers of atherosclerotic disease. Our challenge for the future is to find non-invasive imaging modalities that can predict plaque vulnerability before irreversible damage has occurred. Through early detection and a targeted treatment strategy we hope to reduce the burden of ischemic heart disease.

Reduction of the oxidative injury to the rabbits with established atherosclerosis by protein bound polysaccharide from Coriolus vesicolor

Recent evidence has emerged that macrophage glutathione (GSH) content and selenium dependent glutathione peroxidase (SeGSHPx) activity are inversely related to cell-mediated oxidation of LDL, and intervention means to enhance the macrophage GSH-SeGSHPx status may contribute to attenuation of the atherosclerotic process. Our previous works showed that protein bound polysaccharide (PSK) injected intraperitoneally could enhance SeGSHPx activity and mRNA content of mouse macrophages. The aim of the present study is to demonstrate whether PSK can reduce the oxidative injury to the established atherosclerotic rabbits. Using the established atherosclerotic rabbit model, we studied the effect of PSK on oxidatively modified LDL (Ox-LDL), lipoperoxide (LPO) cholesterol contents and SeGSHPx activities of plasma and tissues (aorta, heart and liver) in the established atherosclerotic rabbits. As compared with the control group, Ox-LDL, LPO and cholesterol contents were much lower; SeGSHPx activities and SeGSHPx/LPO ratios were much higher in plasma and tissues (aorta, heart and liver); and the lesion area of aortae was reduced in the PSK group. Through the increment of SeGSHPx activity in macrophages and aortae, PSK enhances their antioxidation potentiality and improves the antioxidant/prooxidant imbalance in them, and thus decreases Ox-LDL, LPO and cholesterol contents of plasma and tissues, and regresses lesion area of aortae in the established atherosclerotic rabbits.

Shear stress enhances glutathione peroxidase expression in endothelial cells

Hemodynamic forces have profound effects on vasculature. Laminar shear stress upregulates superoxide dismutase (SOD) expression in endothelial cells. SOD converts superoxide anion to H(2)O(2), which, however, promotes atherosclerosis. Therefore, defense against H(2)O(2) may be crucial in reducing oxidative stress. Since glutathione peroxidase (GPx-1) reduces H(2)O(2) to H(2)O, the regulation of GPx-1 expression by mechanical stress was examined. Cultured bovine aortic endothelial cells (BAECs) were subjected to laminar shear stress and stretch force. Shear stress upregulated GPx-1 mRNA expression in a time- and force-dependent manner in BAECs, whereas stretch force was without effect. Furthermore, shear stress increased GPx activity. L-NAME, an inhibitor of nitric oxide synthase, did not affect shear stress-induced GPx-1 mRNA expression. The ability of laminar shear stress to induce GPx-1 expression in endothelial cells may be an important mechanism whereby shear stress protects vascular cells against oxidative stress.

Glutathione S-transferase M1 null genotype is associated with a decreased risk of myocardial infarction

Tobacco smoke is a major cause of both cancer and vascular disease. Although its carcinogenic role via induction of DNA damage and mutation is well established, the mechanisms involved in vascular disease remain unclear. One possibility is that DNA damage causes smooth muscle cell proliferation in the intima of arteries, thereby contributing to atherothrombotic processes. The binding of chemicals to DNA is modulated by detoxification enzymes, including glutathione S-transferases (GST) and microsomal epoxide hydrolase (EPXH). We therefore examined whether polymorphisms in these genes influence risk of cardiovascular disease. Blood was obtained from 398 patients admitted for angiographic investigation of chest pain and 196 age- and sex-matched controls. Patients were subdivided into those with and without previous acute myocardial infarction (AMI). DNA was analyzed for deletions in the GSTM1 and T1 genes and for substitutions in EPXH and GSTP1 genes. The GSTM1 null genotype occurred at a significantly lower frequency in the AMI patient group (48%) compared both to patients with no history of AMI (59%) and to the control group (57.2%). When subjects were stratified for smoking status, a significant association was observed only in smokers, suggesting the polymorphism is more important in the presence of tobacco smoke exposure. The association remained significant after adjusting for age, sex, and stenosis (presence or absence). No significant associations were observed between the other genotypes and cardiovascular disease (chi(2) test; P>0.1). The results of this study indicate that the GSTM1 null genotype is protective against AMI, an effect that is more marked in smokers. However, further study is required in order to elucidate the as yet unexplained, mechanisms underlying this association.

In vitro study of the cytotoxicity of isolated oxidized lipid low-density lipoproteins fractions in human endothelial cells: relationship with the glutathione status and cell morphology

Toxic effects of oxidized lipid compounds contained in oxidized LDL to endothelial cells are involved in the pathogenesis of atherosclerosis. Glutathione (GSH) plays an important role in the redox status of the cell and in the protective effect against oxidant injuries. However, little is known about the respective effect of these different oxidized lipid compounds toward cytotoxicity and GSH status of the cell. In this report, we isolated by high-performance liquid chromatography oxidized lipid compounds from low-density lipoproteins (LDL) oxidized by copper and we examined their effects on cultured endothelial cells. Cytotoxicity and GSH status were determined after incubation of endothelial cells with crude LDL or isolated lipid fractions derived from cholesterol, phospholipids, or cholesteryl esters. Their effects on cell morphology were also assessed. Oxidized lipids coming from cholesteryl esters (hydroperoxides or short-chain polar derivatives) induced a slight but significant GSH depletion without inducing cytotoxicity. The same species coming from phospholipids induced a more pronounced GSH depletion and a cytotoxic effect which is only present for the more polar compounds (short-chain polar derivatives) and corresponding to a total GSH depletion. In contrast, fractions containing oxysterols had a larger cytotoxic effect than their effect on GSH depletion suggesting that their cytotoxic effects are mediated by a GSH-independent pathway. All together, these data suggest that LDL-associated oxidized lipids present in copper-oxidized LDL exert cytotoxicity by an additional or synergistic effect on GSH depletion, but also by another mechanism independent of the redox status of the cell.

Induction of antioxidant stress proteins in vascular endothelial and smooth muscle cells: protective action of vitamin C against atherogenic lipoproteins

Elevated levels of lipid peroxidation and increased formation of reactive oxygen species within the vascular wall in atherosclerosis can overwhelm cellular antioxidant defence mechanisms. Accumulating evidence implicates oxidatively modified low density lipoproteins (LDL) in vascular dysfunction in atherosclerosis and oxidized LDL have been localized with in atherosclerotic lesions. We here report that human oxidatively modified LDL induce expression of 'antioxidant-like' stress proteins in vascular cells, involving increases in the activity of L-cystine transport, glutathione synthesis, heme oxygenase-1 and the murine stress protein MSP23. Moreover, treatment of human arterial smooth muscle cells with the dietary antioxidant vitamin C markedly attenuates adaptive increases in endogenous antioxidant gene expression and affords protection against smooth muscle cell apoptosis induced by moderately oxidized LDL. As vascular cell death is a key feature of atherosclerotic lesions and may contribute to the plaque 'necrotic' core, cap rupture and thrombosis, our findings suggest that the cytoprotective actions of vitamin C could limit plaque instability in advanced atherosclerosis.

Glutathione reverses endothelial dysfunction and improves nitric oxide bioavailability

OBJECTIVES

We investigated whether glutathione (GSH), a reduced thiol that modulates redox state and forms adducts of nitric oxide (NO), improves endothelium-dependent vasomotion and NO activity in atherosclerosis.

BACKGROUND

Endothelial dysfunction and reduced NO activity are associated with atherosclerosis and its clinical manifestations such as unstable angina.

METHODS

In the femoral circulation of 17 patients with atherosclerosis or its risk factors, endothelium-dependent vasodilation with acetylcholine (ACH), and endothelium-independent vasodilation with nitroglycerin and sodium nitroprusside were studied before and after GSH. In 10 patients, femoral vein plasma cyclic guanylate monophosphate (cGMP) levels were measured during an infusion of ACH before and after GSH. Femoral artery flow velocity was measured using a Doppler flow wire and the resistance index (FVRI) calculated as mean arterial pressure divided by flow velocity.

RESULTS

Glutathione strongly potentiated ACH-mediated vasodilation; at the two doses, FVRI decreased by 47% and 56% before, and by 61% and 67% after GSH (p = 0.003). Glutathione also elevated cGMP levels in the femoral vein during ACH infusion from 17.6 +/- 3 to 23.3 +/- 3 pmol/ml (p = 0.006). Augmentation of ACH responses was only observed in patients with depressed endothelial function. Glutathione did not influence endothelium-independent vasodilation with either NO donor.

CONCLUSIONS

Thiol supplementation with GSH selectively improves human endothelial dysfunction by enhancing NO activity.

Thrombosis and coagulation abnormalities in the acute coronary syndromes

The acute coronary syndromes, that include unstable angina, acute myocardial infarction, and many cases of sudden cardiac death, exact a considerable price on society in terms of mortality, morbidity, and health care costs. The coronary atherosclerotic lesion is often an indolent and progressive entity that can destabilize causing an acute syndrome with or without warning. The majority of acute coronary syndromes result from events such as rupture or disruption of the atherosclerotic plaque with intracoronary thrombosis and ischemia of the distal myocardium as a result. Advances in our understanding of the process underlying the acute coronary syndromes has allowed for the identification of targets and rational therapeutic strategies for the prevention and treatment of these syndromes. Many of these therapeutic strategies involve the reversal of prethrombotic forces that often coexist with coronary atherosclerosis. Even with recent advances in our approach to atherosclerosis, intracoronary thrombosis, and the resulting acute coronary syndromes, an unacceptably high event rate persists after these syndromes. Further advances in the prevention and treatment of coronary atherosclerosis and its thrombotic complications depends on a more thorough understanding of the biology of the atherosclerotic plaque and the factors which influence its stability.

Macrophage foam cell formation during early atherogenesis is determined by the balance between pro-oxidants and anti-oxidants in arterial cells and blood lipoproteins

Atherosclerosis is a multifactorial disease, where more than one mechanism, along more than one step, contributes to macrophage cholesterol accumulation and foam cell formation, the hallmark of early atherogenesis. Arterial macrophages take up oxidized low-density lipoproteins (Ox-LDL), leading to cellular accumulation of cholesterol and oxysterols. Atherogenic modifications of LDL include, in addition to oxidation, retention and aggregation. Intervention to inhibit LDL oxidation can affect the above additional LDL modifications. Indeed, we have demonstrated in the atherosclerotic apolipoprotein E-deficient mice that consumption of vitamin E or of flavonoids from red wine or licorice decreased LDL oxidation, LDL retention, and LDL aggregation and attenuated macrophage foam cell formation and atherosclerosis. The balance between pro-oxidants and anti-oxidants in the LDL particle (such as cholesteryl ester vs. vitamin E), as well as in arterial wall macrophages (such as NADPH oxidase vs. glutathione), determines the extent of LDL oxidation. Antioxidants can protect LDL from oxidation not only by their binding to the lipoprotein, but also following their accumulation in cells of the arterial wall. Whereas antioxidants can prevent the formation of Ox-LDL, human serum paraoxonase (PON 1), an HDL-associated esterase that hydrolyzes organophosphates, can eliminate oxidized LDL (by hydrolysis of its lipid peroxides), which is formed when antioxidant protection is not sufficient. Ox-LDL, in turn, can inactivate paraoxonase activity. Thus, the combination of antioxidants together with active paraoxonase decreases the formation of Ox-LDL and preserves PON1's ability to hydrolyze this atherogenic lipoprotein and hence, to attenuate atherosclerosis.